1. Field of the Invention
The present invention relates to a sound processing unit in the transmitter/receiver set of a telephone, wireless equipment, and the like.
2. Description of the Related Art
Earphones and high-directionality microphones are used in conversations between a pilot and a pathfinder in an airport, and in conversations by telephones and wireless equipment in an environment with a high level of noises as a construction field.
However, when the noises are enormous, not only the voices of a persons to be transmitted, but the surrounding noises come in through the earphone and the microphone, so that the partner of the call finds it very difficult to catch the voice of the person transmitting.
In order to solve such a problem, earphone-mic equipment has been proposed, which has a function to detect the voices regardless of the surrounding noises, utilizing vibrations of the internal wall of the external auditory meatus generated when a person speaks, namely, bone conduction sound signals. This earphone-mic houses a vibration pick-up that detects the bone conduction sound signals, and a speaker in the ear piece. This earphone-mic is to be worn on the ear of a user, and is connected through signal lines to a transceiver or a portable telephone.
However, the vibration pick-up of this earphone-mic detects not only the bone conduction sound signals, but also the vibrations generated when the speaker emits sounds. In consequence, the vibrations are transmitted to the other party to the call as an echo, which reduces the quality of conversation.
However, the invention disclosed in the Japanese Patent:Laid-Open publication No. H8-340590 proposes an earphone-mic that suppresses such an echo and improves the quality of conversation. Concretely, this earphone-mic contains, in addition to a speaker and a vibration pick-up, a microphone to detect sounds that the speaker emits; and suppresses the echo in such a manner that a signal detected by the microphone is subtracted from a signal detected by the vibration pick-up.
Here, the level of a signal detected by the microphone is regulated to have the same level as a signal component detected by the vibration pick-up by a frequency equalizer circuit in each frequency band, and then, the signal detected by the microphone is inputted to a subtraction circuit.
However, the voice of the person transmitting is not only detected by the vibration pick-up, but also can be detected in part by the microphone for detecting the output sounds from the speaker. The subtraction of the signal detected by the microphone from the signal detected by the vibration pick-up involves an attenuation of a signal level corresponding to the voices of the person to transmit. This attenuation further increases by the regulation performed by the frequency equalizer circuit.
Further, the conventional earphone-mic that utilizes bone conduction sound signals has to be worn on the user's ear; and there are problems in wearing it and inconvenience in responding during reception.